Plant secondary metabolites (SMs) are not only a useful array of natural products but also an important part of plant defense system against pathogenic attacks and environmental stresses. With remarkable biological activities, plant SMs are increasingly used as medicine ingredients and food additives for therapeutic, aromatic and culinary purposes. Various genetic, ontogenic, morphogenetic and environmental factors can influence the biosynthesis and accumulation of SMs. According to the literature reports, for example, SMs accumulation is strongly dependent on a variety of environmental factors such as light, temperature, soil water, soil fertility and salinity, and for most plants, a change in an individual factor may alter the content of SMs even if other factors remain constant. Here, we review with emphasis how each of single factors to affect the accumulation of plant secondary metabolites, and conduct a comparative analysis of relevant natural products in the stressed and unstressed plants. Expectantly, this documentary review will outline a general picture of environmental factors responsible for fluctuation in plant SMs, provide a practical way to obtain consistent quality and high quantity of bioactive compounds in vegetation, and present some suggestions for future research and development.

Seasonal variations of the phytochemicals contents in needles of T. wallichiana var. mairei due to the effects of growth meteorological parameters were investigated in this study. The needles of T. wallichiana var. mairei were collected from different months and the contents of taxoids (paclitaxel, 10-deacetylbaccatin III (10-DAB), baccatin III, cephalomannine, 10-deacetyltaxol (10-DAT)), flavones (ginkgetin, amentoflavone, quercetin) and polysaccharides were quantified by ultra performance liquid chromatography (UPLC) and the resonance light scattering (RIL) method. The content of taxoids gave the highest level of 1.77 ± 0.38 mg·g⁻¹ in January, and the lowest value of 0.61 ± 0.08 mg·g⁻¹ in September. Unlike taxoids, the content of flavonoids was the highest in August. The content of polysaccharides reached peak value of 28.52 ± 0.57 mg·g⁻¹ in September, which was two times higher than the lowest content of 9.39 ± 0.17 mg·g⁻¹ in January. The contents of paclitaxel, 10-DAB, 10-DAT and polysaccharides significantly depended on meteorological parameters. The mean of minimum temperature (R = −0.61) and length of daylight (R = −0.60) were significantly correlated to 10-DAB content, while 10-DAT level showed significant correlation with length of daylight (R = −0.70) and relative humidity (R = 0.70). In addition, temperature had significantly negative effect on the content of paclitaxel and a significantly positive effect on that of polysaccharides. This study enriched the knowledge on the accumulation pattern of metabolites and could help us to determine the collecting time of T. wallichiana var. mairei for medicinal use.

As a candidate for bioherbicide, 4,8-dihydroxy-1-tetralone (4,8-DHT) was isolated from Caryospora callicarpa epicarp and its two enantiomers, S-(+)-isosclerone and R-(−)-regiolone, were separated by chiral high-performance liquid chromatography (HPLC) on a Chiralcel OD column with chiral stationary phase (CSP)-coated cellulose-tris(3,5-dimethylphenylcarbamate). Then, the phytotoxicity of 4,8-DHT and its enantiomers toward the seeds germination and seedling growth of the five tested plant species, including lettuce (Latuca sativa), radish (Raphanus sativus), cucumber (Cucumis sativus), onion (Allium cepa), and wheat (Triticum aestivum), were investigated and the results indicated a hormesis at low concentration of 4,8-DHT and its enantiomers, but a retardant effect at high concentration. Between the two enantiomers of 4,8-DHT, the S-(+)-isosclerone was more toxic to seeds germination and seedling growth of the five tested plant species than the R-(−)-regiolone, and also the phytotoxicity of S-(+)-isosclerone varied with different plants. For example, S-(+)-isosclerone was the most active to seedling growth of lettuce, indicating that S-(+)-isosclerone had specific effects on different organisms. Thus, all of the chirality and concentration of 4,8-DHT, as well as the affected plant species, need to be taken into consideration in the development and utilization of 4,8-DHT.

Global warming in conjunction with various biotic or abiotic interferences has been jeopardizing the ecosystem of boreal forests. By integrating field inspection with experimental simulation, this work comprehensively investigated the allelopathic effects of a key allelochemical 3,4-dihydroxyacetophenone (DHAP) in the exudates of P. schrenkiana needles on its seed and seedling growth, endogenous hormone metabolism and antioxidant enzyme activity, identified the existence of DHAP allelopathy duality at a certain temperature with an inflection concentration point (e.g. about 0.25 mM at dark/light temperature of 4/12 °C) as the boundary between promotional and inhibitory effect, and verified that the inflection point of DHAP concentration would inevitably shift to a lower level as temperature increased. Consequently, this paper gives a scientific explanation into the intrinsic mechanism of P. schrenkiana degradation due to allelopathy, but also presents a new approach to explore the relationship between forest evolution and global warming. Highlight: A quantitative description on the duality of 3, 4-dihydroxyacetophenone (DHAP) as a promoter or an inhibitor to affect the seed germination, seedling growth and root development of P. schrenkiana , as well as the antioxidant enzyme activities and hormone contents. The new findings of DHAP inflection concentration as boundary to divide the promotional and inhibitory effect of allelopathy which would decrease as environment temperatures rise. An explanation into the intrinsic mechanism of P. schrenkiana degradation due to allelopathy, and a new approach to explore the relationship between forest evolution and global warming.